Dice are random. This sounds quite obvious, but they're perfectly random, and that isn't always fair. Dice cards, however, are both random *and* fair, as they give less randomness over a given set of rolls, but an equivalent amount of randomness over time.
Replacing dice with cards is a controversial, but cards offer lots of other ways to distribute random values rather than the perfect randomness of a dice.
Discard each card and go through the whole deck?
Shuffle after each draw?
Use a shuffle card to shuffle partway through the deck?
Print multiple decks to assemble a custom distribution, with multiple 20s, 1s, or otherwise?
You can get dice cards here:
http://www.drivethrurpg.com/product/229013/Dice-Cards